【摘要】：乙烯是石油化工生產(chǎn)有機(jī)原料的基礎(chǔ)，乙烯產(chǎn)量是衡量一個(gè)國家工業(yè)發(fā)展水平的重要標(biāo)志。近年來我國乙烯工業(yè)得到飛速的發(fā)展和進(jìn)步，但目前仍然存在效率較低、能耗過大等問題，我國的乙烯工業(yè)仍有較大的發(fā)展空間。目前在乙烯裝置常使用的深冷系統(tǒng)有復(fù)疊制冷系統(tǒng)和混合冷劑制冷系統(tǒng)，其中混合冷劑制冷系統(tǒng)主要有二元制冷和三元制冷，本文將重點(diǎn)對乙烯裝置中的深冷系統(tǒng)進(jìn)行分析和優(yōu)化。 本文首先分析某200kt/a乙烯裝置中的用冷需求，將乙烯裝置的深冷分離過程分為變溫冷卻過程和定溫冷凝過程，變溫冷卻過程指的是裂解氣的預(yù)冷過程，定溫冷凝過程指的是乙烯裝置中各塔塔頂冷凝器中的換熱；再分析乙烯-丙烯復(fù)疊制冷系統(tǒng)的換熱集成曲線，可知在裂解氣的預(yù)冷階段，冷熱物流換熱溫差較大。故提出一種組合制冷系統(tǒng)，它集成了純工質(zhì)復(fù)疊制冷和混合冷劑制冷，在各塔塔頂冷凝器中的換熱采用純工質(zhì)復(fù)疊制冷系統(tǒng)，多元混合冷劑制冷系統(tǒng)為乙烯深冷分離的變溫?fù)Q熱過程提供冷量。并用AspenPlus軟件對混合冷劑系統(tǒng)進(jìn)行建模，采用遺傳算法優(yōu)化，得到了節(jié)能21.9%的優(yōu)化結(jié)果。 混合冷劑制冷系統(tǒng)相比于純工質(zhì)制冷系統(tǒng)更適用于大溫程變溫降溫過程，在一定的蒸發(fā)壓力下，通過調(diào)整混合冷劑的配比，可以使冷熱物流曲線匹配得更好，，盡可能減小換熱溫差，減小換熱過程的不可逆損失；還可以簡化設(shè)備，節(jié)省投資。針對混合制冷劑換熱過程復(fù)雜的特點(diǎn)，采用廣泛應(yīng)用的Chen公式和Shah公式計(jì)算混合冷劑的沸騰換熱系數(shù)和冷凝換熱系數(shù)，并將兩組公式聯(lián)立迭代求解計(jì)算乙烯塔頂冷凝器中乙烯蒸氣與三元冷劑的換熱過程。分析結(jié)果可知，混合制冷劑沸騰換熱在干度較小時(shí)換熱系數(shù)小，在干度較大時(shí)換熱系數(shù)大。混合制冷劑的強(qiáng)制對流換熱系數(shù)在流動(dòng)沸騰換熱系數(shù)占主導(dǎo)作用。 某乙烯裝置的深冷系統(tǒng)采用了三元冷劑制冷系統(tǒng)。本文針對該裝置目前運(yùn)行存在的乙烯塔壓過高等問題進(jìn)行分析，并提出串并聯(lián)方式增設(shè)乙烯塔頂板翅式冷凝器的改進(jìn)方案，較好的解決了現(xiàn)有的問題，能使乙烯裝置高效穩(wěn)定安全的運(yùn)行。
[Abstract]:Ethylene is the basis of petrochemical production of organic raw materials, ethylene production is an important indicator of a country's industrial development level. In recent years, China's ethylene industry has made rapid development and progress, but there are still some problems such as low efficiency and excessive energy consumption. At present, the cryogenic systems commonly used in ethylene plants include cascade refrigeration systems and mixed refrigerant refrigeration systems, among which the mixed refrigerant refrigeration systems mainly consist of binary refrigeration and ternary refrigeration. This paper will focus on the analysis and optimization of cryogenic system in ethylene plant. In this paper, the cold requirement of a 200kt/a ethylene plant is analyzed firstly. The cryogenic separation process of the ethylene plant is divided into variable temperature cooling process and constant temperature condensation process. The variable temperature cooling process refers to the precooling process of cracking gas. The process of constant temperature condensation refers to the heat transfer in the top condenser of each tower in ethylene plant, and the analysis of the heat transfer integration curve of ethylene propylene cascade refrigeration system shows that in the precooling stage of cracking gas, the difference of heat exchange temperature between cold and hot material flow is large. Therefore, a combined refrigeration system is proposed, which integrates pure refrigerant cascade refrigeration and mixed refrigerant refrigeration, and uses pure working medium cascade refrigeration system for heat transfer in the top condenser of each tower. The multi-component refrigerant system provides cooling capacity for the variable temperature heat transfer process of ethylene cryogenic separation. The mixed coolant system was modeled by AspenPlus software and optimized by genetic algorithm, and the result of energy saving was 21.9%. Compared with the pure refrigerant refrigeration system, the mixed refrigerant refrigeration system is more suitable for the process of changing temperature and cooling temperature at a large temperature range. Under a certain evaporation pressure, by adjusting the ratio of the mixed refrigerant, the cold and heat flow curves can be matched better. It can reduce the difference of heat transfer temperature, reduce the irreversible loss of heat transfer process, simplify the equipment and save the investment. In view of the complex heat transfer process of mixed refrigerant, the boiling heat transfer coefficient and condensation heat transfer coefficient of mixed refrigerant are calculated by widely used Chen formula and Shah formula. The heat transfer process of ethylene vapor and ternary refrigerant in the top condenser of ethylene tower is calculated by simultaneous iteration of two sets of formulas. The results show that the boiling heat transfer coefficient of mixed refrigerant is smaller when the dryness is small and the heat transfer coefficient is larger when the dryness is larger. The forced convection heat transfer coefficient of mixed refrigerant plays a dominant role in the flow boiling heat transfer coefficient. A ternary refrigerant refrigeration system is used in the cryogenic system of a ethylene plant. This paper analyzes the problems existing in the operation of the plant, such as the high pressure of the ethylene tower, and puts forward an improved scheme of adding the plate-fin condenser on the top of the ethylene tower in series-parallel mode, which solves the existing problems well. Can make ethylene plant efficient, stable and safe operation.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TB657

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